With complex process integration approach and severe fabrication limitations caused by introduction of new materials and diminishing process margins, there are mounting concerns with the increased failure rate at the early life cycle (e.g.<1year operation) of product application known as infant mortality failures. A paradigm change in reliability qualification methodology aim at understanding the impact of variation on reliability is required to ensure reliability robustness. Using Electromigration (EM) as an example, this paper described a methodology where the impact of process variation on reliability is studied. A model that predicts the impact of process variation on EM sigma is also proposed which enables variation and its impact on reliability to be quantified. Using this methodology, the critical process parameters impacting reliability could be identified and controlled to ensure reliability robustness.